Stan Lee, the comic book writer and editor who co-created Spider-Man, the Avengers and the X-Men, has died at the age of 95 in Los Angeles.

Mr. Lee’s impact extended beyond his work in the 1960s writing the origins and early tales of many Marvel Comics characters who now dominate cinema screens—and have become a multibillion-dollar business for
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He also revolutionized his industry by bringing real-world problems to the stories of spandex-clad superheroes for the first time.

Stan Lee: A Life in Pictures

He co-created such iconic characters as Spider-Man, the Avengers, and the X-Men

In 1978, Stan Lee speaking with Nicholas Hammond, right, who played Spider-Man in the 1970s TV show—a character that Mr. Lee cocreated.

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In 1978, Stan Lee speaking with Nicholas Hammond, right, who played Spider-Man in the 1970s TV show—a character that Mr. Lee cocreated.

CBS/Getty Images

An energetic salesman who loved the public eye, he tirelessly promoted comic books as an integral piece of American pop culture that deserved to be taken seriously. In the process, he became their best-known creator with the general public.

“He was the gold standard as the ambassador for comic books,” said Jim Lee, a longtime Marvel artist who is now co-publisher of competitor DC Comics, part of AT&T Inc.’s WarnerMedia. He isn’t related to Stan Lee.

Mr. Lee remained an avuncular and beloved advocate of comic books and his own business ventures well into his 90s, attending fan conventions until recently even as his health appeared to decline.

From the Archive: Video Interview With Stan Lee

Stan Lee, creator of characters such as Spider-Man and the X-Men, discusses his legendary career as a pioneer in the comic industry in this interview from October 2010.

Born Stanley Lieber in New York City, Mr. Lee grew up poor and lonely during the Great Depression and spent much of his time escaping in books, he wrote in his 2015 illustrated memoir, “Amazing Fantastic Incredible.” In 1939, he got a job as an office assistant at Timely, later renamed Marvel, and soon started writing stories for characters including Captain America and editing the company’s entire line of comic books.

Following service in World War II, Mr. Lee kept writing and editing comics books for decades but didn’t make his mark until 1961, when Marvel’s publisher asked him to imitate the success of DC’s “Justice League” by coming up with a new superteam. Mr. Lee’s creation, the Fantastic Four, broke the mold of flawless and unrelatable super-beings that had long defined the genre.

The Fantastic Four, by contrast, were family members who bickered and considered their powers more curse than blessing.

The quartet were an instant sales success and were quickly followed by other superheroes with very human problems including Spider-Man, a geeky teenager who worried about girls and bullies, and the X-Men, a team of misunderstood “mutants” widely viewed as a metaphor for oppressed minority groups.

“This was coming at a time when the baby boomers were teenagers,” Lee biographer Tom Spurgeon told the website Vulture in 2016. “If Stan hadn’t been doing those stories that were for teenagers and not children, comics would have disappeared.”

In addition to writing and editing his comics, Mr. Lee spoke directly to fans in columns and letter pages with an enthusiastic, personable voice that made readers feel like they knew him. He finished his missives with a word that became indelibly linked to him: “Excelsior!”

Mr. Lee collaborated with several of the industry’s best-known artists during his heyday at Marvel in the 1960s. His most famous—and ultimately troubled—relationship was with Jack Kirby, who drew the first appearances of the Fantastic Four and the Hulk, among others. Upset in part about the enormous amount of attention heaped upon Mr. Lee in the media, but denied him, Mr. Kirby decamped to DC in 1970. In a 1990 interview with Comics Journal, Mr. Kirby said Mr. Lee’s only role in their collaborations was as an editor, charging: “I’ve never seen Stan Lee write anything.”

In his memoir, Mr. Lee praised the work of Mr. Kirby, who died in 1994, and wrote that he never understood why their relationship soured, noting, “It’s hard to correct a misunderstanding if you don’t know what it is that’s misunderstood.”

Questions about creator credit on many of Marvel’s most famous characters have only been exacerbated by “the Marvel method,” a creative process used by the overworked Mr. Lee in which he wrote plot outlines and allowed artists to work out the details of the story while they drew. Mr. Lee later filled in dialogue.

By the 1970s, Mr. Lee’s official title was “publisher,” but he became more of an elder statesman at Marvel. He spent much of his time speaking about comic books on college campuses and around the world. As his prominence rose, he immersed himself in celebrity culture and collaborated on comic books with Paul McCartney and the rock band Kiss.

In the 1980s, Mr. Lee moved to Los Angeles in an attempt to boost the presence of Marvel characters in movies, television and animation, but found little success. He had no involvement in the wave of Marvel-based movies that began with 2000’s “X-Men,” save for cameos that fans came to love. He played a mailman in 2005’s “Fantastic Four,” a Hugh Hefner look-alike in 2008’s “Iron Man,” and a DJ at a strip club in 2016’s “Deadpool.”

Mr. Lee spent much of the past two decades on new business ventures outside of Marvel. An internet company founded in 1998, Stan Lee Media, was meant to produce animated video based on its namesake’s creations, but filed for bankruptcy under a cloud of controversy two years later. “It ended badly and the less said, the better,” Mr. Lee wrote in his memoir.

Beginning in 2001, Mr. Lee was chairman and chief creative officer of POW! Entertainment, which aimed to exploit his new creations throughout media. But the company struggled for years and none of those characters, such as crime-fighting exotic dancer Stripperella, have had anything close to the success of his work at Marvel. Mr. Lee earlier this year filed a lawsuit against POW! for alleged fraud that was quickly dropped.

“You wouldn’t think 50 years later you have to keep proving yourself, but Stan in his 90s was a bundle of energy who had to keep moving forward,” said Marv Wolfman, a comic-book writer and former editor in chief of Marvel.

Mr. Lee’s wife of 70 years, Joan, died last year. He is survived by a daughter, also named Joan and known as J.C.